Hurricane BILL (Text)

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HURRICANE BILL DISCUSSION NUMBER 8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009
500 AM AST MON AUG 17 2009
INFRARED SATELLITE PICTURES REVEAL AN IMPRESSIVE MASS OF DEEP
CONVECTION...WITH A LARGE AREA OF -70C AND EVEN -80C CLOUD
TOPS WITHIN A WELL-ORGANIZED CENTRAL DENSE OVERCAST. IN
ADDITION...SEVERAL WELL-DEFINED BANDS ARE NOTED OUTSIDE OF THE
CENTRAL CONVECTIVE CORE. A 0142 UTC TRMM PASS INDICATED A DISTINCT
CONVECTIVE RING AROUND THE CENTER...ALSO SUGGESTIVE OF INCREASED
ORGANIZATION. DVORAK T-NUMBERS ARE AT 4.0 FROM TAFB AND SAB...ALONG
WITH CURRENT TRENDS...SUPPORT INCREASING THE INITIAL INTENSITY TO
65 KT. THIS MAKES BILL THE FIRST HURRICANE OF THE 2009 ATLANTIC
HURRICANE SEASON.
RECENT SATELLITE CENTER FIXES ARE LESS DOUBTFUL THAN EARLIER AND
YIELD A RATHER RAPID INITIAL MOTION ESTIMATE OF 285/19. GLOBAL
MODELS ARE IN GOOD AGREEMENT ON A GENERAL WEST-NORTHWEST TRACK FOR
THE NEXT DAY OR TWO...AS BILL IS STEERED BY A DEEP-LAYER RIDGE
NORTHEAST OF THE CYCLONE. HOWEVER...WATER VAPOR IMAGERY SHOWS A
WEAKNESS CURRENTLY ALONG 50W...WHICH IS FORECAST TO BEGIN ERODING A
PORTION OF THE SUBTROPICAL RIDGE OVER THE CENTRAL ATLANTIC OVER THE
NEXT 48 HOURS. AS THE BREAK IN THE RIDGE BECOMES MORE
SUBSTANTIAL...A MAJORITY OF THE MODEL GUIDANCE TURNS BILL ON A MORE
NORTHWESTWARD COURSE LATE IN THE FORECAST PERIOD. THE ONE EXCEPTION
IS THE UKMET WHICH INSISTS ON A MORE SOUTHERN SOLUTION. THE
OFFICIAL TRACK IS INITIALLY NUDGED SLIGHTLY SOUTHWARD IN THE
SHORT-TERM TO ACCOUNT FOR A MORE CERTAIN INITIAL POSITION...BUT
LITTLE CHANGE WAS MADE TO THE PREVIOUS TRACK THEREAFTER.
BILL IS EXPECTED TO TRACK THROUGH AN ENVIRONMENT CHARACTERIZED BY
LOW SHEAR AND SEA SURFACE TEMPERATURES JUST UNDER 27C THROUGH 24
HOURS. SIMILAR TO BEFORE...THE GFDL/HWRF INDICATE A NEARLY FLAT
RATE OF INTENSIFICATION FOR THE NEXT DAY OR TWO...PERHAPS
REFLECTING MARGINALLY WARM WATERS. IN SPITE OF THIS...THE SHIPS
RAPID INTENSIFICATION INDEX HAS CONTINUED FORECASTING A RATHER HIGH
PROBABILITY OF A 30 KT INTENSITY INCREASE DURING THE NEXT 24 HOURS.
THEREAFTER...ALL INTENSITY GUIDANCE INDICATES A CONDUCIVE
ENVIRONMENT FOR STRENGTHENING...WHICH SHOULD ALLOW BILL TO BECOME A
MAJOR HURRICANE. THE OFFICIAL FORECAST FOLLOWS SUIT...CLOSEST TO
THE SHIPS MODEL GUIDANCE. TOWARD THE END OF THE FORECAST
PERIOD...SEVERAL OF THE RELIABLE GLOBAL MODELS SUGGEST INCREASING
WESTERLY SHEAR AS BILL IS SEPARATED FROM ITS FAVORABLE...UPPER-
LEVEL SUPPORT. CONSEQUENTLY...THE OFFICIAL INTENSITY FORECAST
INDICATES MINOR WEAKENING NEAR THE END OF THE PERIOD.
IT APPEARS AS IF THE CENTER OF BILL WILL PASS VERY CLOSE TO NOAA
BUOY 41041 LATER THIS MORNING.
FORECAST POSITIONS AND MAX WINDS
INITIAL 17/0900Z 13.8N 44.0W 65 KT
12HR VT 17/1800Z 14.4N 46.4W 75 KT
24HR VT 18/0600Z 15.1N 49.0W 85 KT
36HR VT 18/1800Z 16.0N 51.6W 95 KT
48HR VT 19/0600Z 17.3N 54.0W 105 KT
72HR VT 20/0600Z 20.5N 59.0W 110 KT
96HR VT 21/0600Z 25.0N 63.5W 105 KT
120HR VT 22/0600Z 30.1N 66.5W 100 KT
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FORECASTER KIMBERLAIN
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